Ether generation from acetone

Abstract: A process for the generation of diisopropyl ether from a crude by-product acetone stream comprises the steps of: a) hydrogenating a crude acetone stream over a bulk-metal, nickel-rich catalyst to give an isopropanol-rich intermediate, and b) dehydrating said isopropanol-rich intermediate in the presence of strong acid zeolite catalyst to yield diisopropyl ether. Preferably, the strong acid zeolite catalyst used in the second step is selected from the group consisting of β-zeolite, optionally modified with one or more metals from Group IB, VB, VIB, VIIB and VIII of the Periodic Table, and a dealuminised Y-zeolite. The disclosed method may also be used for the co-generation of diisopropyl ether with methyl t-butyl ether if the crude acetone stream contains, in addition, significant quantities of methanol and t-butanol.

Description: The present invention concerns a novel two-step procedure for generation of diisopropyl ether (DIPE), and also for co-generation of DIPE and methyl t-butyl ether (MTBE), from a crude by-product acetone stream which comprises the steps of: (1) hydrogenating the crude acetone stream over a bulk-metal nickel-rich catalyst to give an isopropanol-rich effluent; and (2) subjecting the isopropanol-rich intermediate to dehydration conditions in the presence of strong acid zeolite catalyst, preferably from the group consisting of a β-zeolite, dealuminised Y-zeolite and metal-modified β-zeolites, to yield DIPE or a mixture of DIPE and MTBE, depending on the composition of the crude acetone stream. It is known to those skilled in the art that ethers, including both symmetrical and unsymmetrical ethers, may be prepared by reacting an alcohol with another alcohol to form the desired product. The reaction mixture, containing catalyst and/or condensing agent may be separated and further treated to permit attainment of the desired product. Such further treatment commonly includes one or more distillation operations. Methyl tert-butyl ether is finding increasing use as a blending component in high octane gasoline as the current gasoline additives based on lead and manganese are phased out. Currently all commercial processes for the manufacture of methyl tert-butyl ether are based upon the liquid-phase reaction of isobutylene and methanol (Eq. 1), catalyzed by a cationic ion-exchange resin (see, for example: Hydrocarbon Processing, Oct. 1984, p. 63; Oil and Gas J., Jan. 1, 1979, p. 76; Chem. Economics Handbook-SRI, Sept. 1986, p. 543-7051P). The cationic ion-exchange resins used in MTBE synthesis normally have the sulphonic acid functionality (see: J. Tejero, J. Mol. Catal., 42 (1987) 257; C. Subramamam et al., Can. J. Chem. Eng., 65 (1987) 613). With the expanding use of MTBE as an acceptable gasoline additive, a growing problem is the availability of raw materials. Historically, the critical raw material is isobutylene (Oil and Gas J., June 8, 1987, p. 55). It would be advantageous, therefore, to have a process to make MTBE that does not require isobutylene as a building block. DIPE may be used in addition to MTBE as an octane enhancer in gasoline. Japanese Patent Application No. 82-07432 teaches the use of zeolites, particularly mordenites and faujasites, to make dialkyl ethers containing primary or secondary alkyl groups by the liquid phase dehydration of alcohols. U.S. Patent No. 4,058,576 teaches the use of (pentasil-type) aluminosilicate zeolites, such as ZSM-5, having a pore size greater than 5 angstrom units (> 0.5 nm) and a silica-to-alumina ratio of at least 12, to convert lower alcohols to a mixture of ethers and olefins. In U.S. Patent No. 5,214,217 there is disclosed a method for preparing methyl tertiary butyl ether by reacting butanol and methanol in the presence of a catalyst comprising a super-acid alumina or a faujasite-type zeolite. In European Patent No. 0 323 138 there is disclosed a catalytic process for converting light olefins to ethers suitable as high octane blending stocks carried out by contacting the olefin, especially propene, with water and alcohol recovered from a downstream distillation operation in an olefin conversion unit in the presence of an acidic zeolite catalyst. In this work diisopropyl ether (DIPE) was prepared from C 3 H 6 and aqueous iso-PrOH in the presence of silica-bound zeolite Beta catalyst at 166°C. None of the aforementioned references suggests the possibility of conversion of the acetone portion present in a by-product stream into useful oxygenates. The portion of said by-product stream which typically comprises acetone is about 20% to 80%. It would greatly enhance the economics of any process to produce MTBE or other oxygenates if acetone from a by-product stream could be converted to useful oxygenate products such as diisopropyl ether (DIPE). In order to meet the above object, the invention provides a process for generation of diisopropyl ether from a crude by-product acetone stream, which process comprises: (1) hydrogenating a crude acetone stream over a bulk-metal nickel-rich catalyst to give an isopropanol rich intermediate, and (2) dehydrating the isopropanol-rich intermediate in the presence of strong acid zeolite catalyst to yield diisopropyl ether. The invention also encompasses the co-generation of methyl t-butyl ether and diisopropyl ether by the steps indicated above. To enable such co-generation, the by-product acetone stream must contain, in addition, significant quantities _ that is preferably greater than 5% _ of both methanol (MeOH) and t-butanol (tBA). Most preferably, for the co-generation of DIPE and MTBE, the crude acetone feed contains 10%-40% each of both methanol and t-butanol. The two-step DIPE synthesis can be represented by: In industrial processes to make propylene oxide, a large number of by-products are typically generated with the desired product. The by-products may include formic acid, acetic acid, their ester derivatives, t-butanol and acetone. Acetone may constitute about 20% to 80% of certain crude by-product streams. These crude acetone streams may be further mixed with methanol. In the first step of the process according to the invention, the crude acetone is passed over a nickel-rich catalyst. A preferred nickel catalyst is characterised by having the composition, calculated in mole percent, of about 60%-85% nickel, 1%-30% copper and 0.1%-6% chromium, with the most preferred proportions being about 65%-78% nickel, 10%-20% copper and 1%-3% chromium. The temperature necessary to achieve the desired acetone hydrogenation to isopropanol (IPA) is >100°C, the preferable range being 120°-180°C. The conversion of acetone to isopropanol in the first step (Eq. 2) is normally >90% per pass in continuous processing and, preferably, it is 99% or more. In the second step, the isopropanol is subjected to dehydration conditions in the presence of strong acid zeolite catalyst, preferably one or more from the group consisting of β-zeolite, optionally further modified with one or more metals, or a dealuminised Y-zeolite. The preferred forms of zeolite beta are the highly acidic, high silica forms, having a silica-to-alumina mole ratio of at least 10:1, and preferably in the range of 10:1 to 50:1 in the as-synthesized form, and a surface area of at least 100 m 2 /g. Suitable β-zeolites for the practice of this invention include Valfor C806β, Valfor CP815β and Valfor C861. Valfor® is the registered trademark of the PQ Corporation. Valfor® C806β zeolite is zeolite beta powder in template cation form. It is a high silica shape selective zeolite which contains the organic template used in the crystallisation step, having been isolated after filtration and washing of the synthesis product. C806β has a SiO 2 /Al 2 O 3 molar ratio of 23-26; the crystal size is 0.1-0.7 µm; the surface area after calcination is 700-750 m 2 /g; the cyclohexane adsorption capacity after calcination is 19-24g/100g; Na 2 O content is 0.01-1.0% by weight anhydrous, and the organic content is 11-13% by weight, on a water-free basis. Valfor® C815β zeolite is a calcined zeolite beta powder in hydrogen, sodium form. It is similar to C806β except the product has been calcined to decompose the organic template. C815β is a high silica, shape selective aluminosilicate with a large pore diameter. C815β also has a SiO 2 /Al 2 O 3 molar ratio of 23-26; the crystal size, surface area, cyclohexane adsorption capacity and Na 2 O are all within the same ranges as given above for C806β. Valfor® C861β is an extrudate made of 80% C815β powder and 20% alumina powder. Optionally, said β-zeolites may be modified with a halogen, a halogen-containing organic compound, or a halogen-containing acid. Said halogen may be fluorine, chlorine, bromine or iodine, but is preferably fluorine. In the case of fluoride treatment, the fluoride content of the treated β-zeolite may be in the range of 0.1 to 10 wt%, but preferably is about 1%. Optionally, said fluoride-treated zeolites may be calcined, at temperatures of 200°C and above, prior to further usage or modification. Said catalysts may be formed in the presence of a binder, such as a Group III or Group IV oxide. The Group III or Group IV oxides used in conjunction with said β-zeolite include oxides of aluminium, silicon, titanium, zirconium, hafnium, germanium, tin and lead, as well as combinations thereof. Alumina is preferred. Said binders may comprise 10% to 90% of the formed catalyst. Particularly effective for co-generation of MTBE and DIPE are the β-zeolites modified with multiple metals. The metals useful for modifying the zeolite in the present invention comprise those from Groups IB, VB, VIB, VIIB and VIII of the Periodic Table. Preferred metals are those found in Groups IB, VIB, VIIB and VIII of the Periodic Table and include copper, chromium, manganese, iron, nickel, palladium and platinum. Especially good results are observed using combinations of iron, manganese and chromium or combinations of nickel and copper on VALFOR® Zeolite 861β. Said zeolites are preferably impregnated with said specified metals as their salts, particularly their metal nitrate or chloride salts, in an aqueous, alcoholic, or ketonic media over a period of 1-24 hours, then the solids are filtered off, dried at elevated temperature, e.g. 120°C, for a period of time and calcined at 300-800°C for a further period, e.g. 315°C for 2 hours, followed by 540°C for another 2 hours, then reduced in a stream of hydrogen at ≥200°C. The amount of the various metals deposited on the zeolite can vary. The amount of each individual metal, i.e., iron, chromium, copper, manganese, and nickel, can vary from 0.01 to 10.0%. Where iron, chromium and manganese are deposited on 861β the preferred weight proportion is from 0.1% to 5.0%. The second type of catalyst suitable for the second stage of this invention generally comprise dealuminised Y-zeolite catalysts. The preferred catalysts for use in the dealuminised form for the reaction of Eq. 2 are certain crystalline aluminosilicate zeolites, particularly the isostructural group of faujasite zeolites that include the synthetic X- and Y-zeolites. The preferred zeolites for dealuminisation are the Y-zeolites. The unit cells of faujasite zeolites are cubic, a o ≈ 2.5 nm, and each contains 192 silicon- or aluminium-centred oxygen tetrahedra which are linked through shared oxygen atoms. Because of the net negative charge on each of the aluminium-centred tetrahedra, each unit cell contains an equivalent number of charge-balancing cations. These are exclusively sodium ions in zeolites in their synthesized form. Typical cell contents for the Y-zeolites in the hydrated form are: Na 56 [(AlO 2 ) 56 (SiO 2 ) 136 ] x ·250 H 2 0 Y-zeolites are distinguished on the basis of the relative concentration of silicon and aluminium atoms and the consequent effects on detailed structure and related chemical and physical properties. The aluminium atoms in the unit cell of Y-zeolite vary from 76 to 48, resulting in a Si:Al ratio between 1.5 and 3.0. Both the cation concentration and charge density on the aluminosilicate structure are lower for Y-zeolites than for X-zeolites, where the aluminium atoms in the unit cell vary from 96 to 77. It has been demonstrated in the present invention that these Y-zeolites are particularly effective in the dealuminised form. Preferably, said Y-zeolites are dealuminised by ammonium exchange followed by calcination, or by treatment with ethylenediaminetetraacetic acid (EDTA) or other chelating agents, or by treatment with fluorine or a fluorine-containing compound such as silicon tetrafluoride or ammonium fluorosilicate, or by hydrothermal treatment and/or acid treatment. Said dealuminised Y-zeolites should have a silica-to-alumina molar ratio of greater than three, preferably a ratio of 5 or greater and most preferably a silica-to-alumina ratio of 5 to 100. The examples demonstrate the usefulness of catalysts having a silica-to-alumina ratio of 5 to 25 and particularly 5 to 10. Examples of suitable commercially available dealuminised Y-zeolites include UOP's LZY-82 and LZY-72, PQ Corporation's CP-304-37 and CP-316-26, UOP's Y-85, Y-84, LZ-10 and LZ-210. The unit cell size and SiO 2 /Al 2 O 3 molar ratio for typical dealuminised Y-zeolites are noted in the following table: ZEOLITE TYPE UNIT CELL SIZE, A SiO 2 /Al 2 O 3 MOLAR LZY-82 24.53 7.8 Said catalysts may be in the form of powders, pellets, granules, spheres, shapes and extrudates. The examples described herein demonstrate the advantages of using extrudates. The reaction may be carried out in either a stirred slurry reactor or in a fixed bed continuous flow reactor. The catalyst concentration should be sufficient to provide the desired catalytic effect. Dehydration to DIPE can generally be conducted at temperatures from 20° to 250°C; the preferred range is 80° to 200°C. Good results are observed throughout this temperature range. However, it can be noted that the best conversion figures for MTBE, DIPE co-generation are observed when the temperature is 120°-180°C. The total operating pressure may be from 0.1 to 35 MPa (0 to 5000 psig), or higher. The preferred pressure range is 0.7 to 7 MPa (100 to 1000 psig). Typically, DIPE is generated continuously in up to ca. 13 wt% concentration or greater in the crude liquid product at total liquid hourly space velocities (LHSV) of up to 6 or higher and relatively mild conditions, where: LHSV = Volume Of Total Liquid Feed Run Through The Reactor Per Hour Volume Of Catalyst In Reactor Conversions of isopropanol (IPA) are estimated in the following examples using the equation: (Mole% of IPA in Feed - Mole% of IPA in Product) Mole% of IPA in Feed x 100 The examples which follow illustrate the two-step synthesis of MTBE and DIPE from acetone also containing methanol plus t-butanol using β-zeolites, optionally modified with multiple metals, or dealuminised Y-zeolites. Specifically, accompanying examples illustrate: 1) The hydrogenation of crude acetone by-product stream from a PO/MTBE unit over a bulk metal, nickel-rich catalyst under moderate conditions (See Example 1). 2) The co-generation of DIPE/MTBE from the hydrogenated acetone stream of Example 1 using a β-zeolite catalyst (See Example 2). 3) DIPE/MTBE generation from the hydrogenated acetone stream of Example 1 using: a. A palladium-impregnated, fluorided β-zeolite (Example 3, Table 3). b. An iron, chromium, manganese-modified β-zeolite (Example 4, Table 4). c. A platinum-impregnated β-zeolite (Example 5, Table 5). d. A nickel, copper-treated β-zeolite (Example 6, Table 6). e. A dealuminised Y-zeolite, LZY-84 (Example 7, Table 7). EXAMPLE 1 This example illustrates the hydrogenation of a crude acetone stream. A crude acetone mix from a PO/MTBE unit containing 62% acetone plus significant quantities of methanol and t-butanol and having the composition shown in Table 1 was passed, upflow, over a nickel, copper, chromium bulk metal catalyst containing about 72% nickel (Ni 2715, 3.2 mm (1/8") Tablets from Engelhard Corp.) in the presence of hydrogen (90 1/hr) at LHSV of 0.5 at a series of temperatures (120°-160°C). Hydrogenation of said stream was achieved at 160°C and a typical product composition for the liquid fraction is given in Table 1 below. CRUDE ACETONE HYDROGENATION Ex. Catalyst Temperature (°C) LHSV Sample Composition (%) MeOH Me 2 CO IPA tBA tBF ATBP 1 Ni 2715 3.2 mm T FS-1 13.9 61.7 0.1 16.7 0.1 3.3 160 0.5 1 15.8 0.8 48.3 30.8 - - EXAMPLE 2 This example illustrates the co-generation of diisopropyl ether (DIPE) and methyl t-butyl ether (MTBE) from a hydrogenated acetone feedstock. Synthesis was conducted in a tubular reactor (12.5 mm i.d., 250 mm long) constructed of 316 stainless steel, operated upflow, and mounted in a furnace, controllable to ±1.0°C, and fitted with pumps allowing flow control to <1 cc/hr. The reactor was also fitted with a pressure regulating device and equipment for monitoring temperature, pressure and flow rate. The reactor was charged at the beginning of the experiment with 50cc of β-zeolite (80% beta, 20% alumina binder, in 1.6 mm (1/16") diameter extruded form, C861β from PQ Corp.). A glass wool screen was placed at the top and bottom of the reactor to ensure the catalyst would remain in the middle portion. The catalyst bed was treated with the crude hydrogenated acetone feedstock of Example 1, while the reactor was held at a series of temperatures (120°-180°C). Total unit pressure was maintained at 5.2 MPa (750 psi). Samples of crude product effluent were collected periodically on stream, in 316ss bombs, and analyzed by glc and gc-ms. Typical analyses data are summarized in Table 2. At 180°C, the isopropanol conversion level is 67% (Sample 6). At 120°C, the major product is methyl t-butyl ether (MTBE). At 180°C, the major products are diisopropyl ether (DIPE), methyl isopropyl ether (MIPE), plus some isopropyl t-butyl ether (IPTBE). Another co-product is diisobutylene (C 8 H 16 ). EXAMPLE A The example illustrates the preparation of a multimetal-modified β-zeolite. To 102g of β-zeolite (Valfor C861β, 80% β-zeolite, 20% alumina) in 1.6 mm (1/16") diameter extruded form was added a solution of ferric chloride hydrate (1.04g), chromium(II) nitrate, hydrate (1.64g) and manganese(II) nitrate hydrate (1.10g) in 92cc of distilled water. Impregnation of the β-zeolite was allowed to occur over 1-2 hours, then the solids were filtered off, dried at 120°C overnight, and calcined at 315°C for 2 hours, followed by 540°C for another 2 hours. The recovered green solid extrudates showed the presence of: %Fe = 0.27 %Cr = 0.19 %Mn = 0.08 Acidity = 0.35 meq/g EXAMPLES 3-7 These examples illustrate the co-generation of DIPE and MTBE using a series of metal-modified beta and dealuminised Y-zeolite catalysts. Following the procedures and using the equipment of Example 2, a series of metal-modified beta and dealuminised Y-zeolite catalysts were used to co-generate DIPE and MTBE from the hydrogenated acetone stream of Example 1. Co-generation of DIPE/MTBE was demonstrated using: a) A palladium-impregnated, fluorided β-zeolite (Table 3). b) An iron, chromium, manganese modified β-zeolite (Table 4). c) A platinum-impregnated β-zeolite (Table 5). d) A nickel, copper treated β-zeolite (Table 6). e) A dealuminised Y-zeolite (Table 7). This application is related to United States Patents 4,822,921; 4,827,048; 5,099,072; 5,081,318; 5,059,725; 5,157,162; 5,162,592; 5,157,161; 5,183,947; 5,214,217; 5,214,218, 5,220,078 and 5,364,981. It is also related to European Patent Application No. 0 624 564.

Claims: A process for the generation of diisopropyl ether from a crude by-product acetone stream, which process comprises: a) hydrogenating a crude acetone stream over a bulk metal, nickel-rich catalyst to give an isopropanol-rich intermediate, and b) dehydrating the isopropanol-rich intermediate in the presence of strong acid zeolite catalyst to yield diisopropyl ether. A process as claimed in claim 1 wherein the nickel-rich catalyst comprises 60%-85% nickel, 1%-30% copper and 0.1%-6% chromium. A process as claimed in claim 1 or claim 2 wherein the crude by-product acetone stream contains 20 to 80 % acetone. A process as claimed in any preceding claim wherein, in the first stage, the acetone is hydrogenated in the temperature range 120 to 180 °C. A process as claimed in any preceding claim wherein, in the second stage, the generation of diisopropyl ether is carried out in the temperature range 80 to 200 °C. A process as claimed in any preceding claim wherein a β-zeolite catalyst is used having a silica:alumina molar ratio of at least 10:1. A process as claimed in claim 6 wherein the β-zeolite has a surface area, after calcination, of at least 100 m 2 /g. A process as claimed in claim 6 or claim 7 wherein the β-zeolite is modified with one or more metals from Groups IB, VIB, VIIB and VIII of the Periodic Table. A process as claimed in any one of claims 6 to 8 wherein said β-zeolite is treated with a fluoride-containing compound. A process as claimed in any one of claims 6 to 9 wherein said β-zeolite is formed in the presence of a binder selected from a Group III oxide or a Group IV oxide. A process as claimed in any one of claims 1 to 5 wherein the second stage catalyst is a Y-zeolite dealuminised in a manner selected from: a) ammonium exchanging the Y-zeolite followed by calcination; b) treating the Y-zeolite with ethylenediaminetetraacetic acid. c) treating the Y-zeolite with a fluorine-containing compound from the group consisting of silicon tetrafluoride and ammonium fluorosilicate; or d) treating the Y-zeolite with steam, optionally followed by acid treatment. A process for the generation of diisopropyl ether as claimed in any preceding claim wherein said acetone stream also contains significant quantities of both methanol and t-butanol, and wherein methyl t-butyl ether is generated as a co-product with said diisopropyl ether. A process as claimed in claim 12 wherein the methanol and t-butanol contents of the acetone by-product stream are in the range 10% to 40% in proportions by weight.

Inventors: DAI PEI-SHING EUGENE, KNIFTON JOHN FREDERICK, DAI, PEI-SHING EUGENE, KNIFTON, JOHN FREDERICK
Applicants: HUNTSMAN SPEC CHEM CORP, HUNTSMAN SPECIALTY CHEMICALS CORPORATION
Application year: 1994
Main classification: C07C43
IPC codes: B64B1, C07C41, B01J23, C07C43, B01J29, C07B61, C07C29, C07C31, B64C1